It is known that for certain metallic films deposited on a surface of an integrated circuit wafer, the sheet resistance of the film will vary inversely with its thickness. For this reason, sheet resistance measurements are often made of semiconductor wafers after the completion of a selected metallic film deposition step to determine if the deposition parameters of the step are correct. The sheet resistance measurement is usually performed by the application of a plurality of probes, a first two of which are connected to a current source and voltage supply in series and a second two of which, which may be the same or different from the first two probes, are connected to a voltmeter. The voltmeter reading may be used to determine the sheet resistance by a predetermined formula depending on the electrical configuration of the probes. From the sheet resistance and the bulk resistivity, the thickness of the film may be determined.
In conventional reactors, no method has been developed to measure the sheet resistance in situ while the deposition process is occurring, and therefore the operator must guess when the metallic deposition step should be ended. The film deposition parameters must therefore be arrived at by a cut-and-try method that uses further time and materials, and which may not be reliable if a variance in one of the process parameters goes unnoticed. A need has therefore arisen for determining film thickness by measuring a sheet resistance of an integrated circuit wafer in situ.